Communication system

ABSTRACT

A communication system is presented in which a base station is provided for communicating with a plurality of mobile communication devices in a cellular communication system. The base station operates one of more communication cells and communicates subframes, with each of the plurality of communication devices within the cell(s), each comprising the communication resources of a control region for communicating a control channel and the communication resources of a data region for communicating a respective data channel. The base station communicates a control channel having a first DMRS sequence in a control region of some subframes and a control channel having a second DMRS sequence in a control region of other subframes. The second control channel may be transmitted in a radio beam focussed spatially in a direction of a communication device. The first control channel may be transmitted omnidirectionally throughout the cell(s).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/893,736 filed on Jun. 5, 2020, which is acontinuation application of U.S. patent application Ser. No. 14/993,636filed on Jan. 12, 2016, which is issued as U.S. Pat. No. 10,716,103,which is a continuation application of U.S. patent application Ser. No.13/818,294 filed on Feb. 21, 2013, which is issued as U.S. Pat. No.9,271,272, which is a National Stage Entry of international applicationPCT/JP2012/069523 filed on Jul. 25, 2012, which claims the benefit ofpriority from UNITED KINGDOM Patent Application 1112752.9 filed on Jul.25, 2011, the disclosures of all of which are incorporated in theirentirety by reference herein.

TECHNICAL FIELD

The present invention relates to mobile communications devices andnetworks, particularly but not exclusively those operating according tothe 3^(rd) Generation Partnership Project (3GPP) standards orequivalents or derivatives thereof. The invention has particularalthough not exclusive relevance to the Long Term Evolution (LTE) ofUTRAN (called Evolved Universal Terrestrial Radio Access Network(E-UTRAN)).

BACKGROUND ART

It has been decided, as part of the 3GPP standardisation process, thatdownlink operation for system bandwidths beyond 20 MHz will be based onthe aggregation of a plurality of component carriers at differentfrequencies. Such carrier aggregation can be used to support operationin a system both with and without a contiguous spectrum (for example, anon-contiguous system may comprise component carriers at 800 MHz, 2 GHz,and 3.5 GHz). Whilst a legacy mobile device may only be able tocommunicate using a single, backward compatible, component carrier, amore advanced multi-carrier capable terminal would be able tosimultaneously use the multiple component carriers.

Carrier aggregation can be particularly beneficial in a heterogeneousnetwork (HetNet), even when the system bandwidth is contiguous, and doesnot exceed 20 MHz because multiple carriers enable interferencemanagement between different power class cells as well as open accessand closed subscriber group (CSG) cells. Long-term resource partitioningcan be carried out by exclusively dedicating carriers to a certain powerclass of cell (Macro/Pico/CSG).

Further, the need for interference management between different cellsoperating on component carriers of the same frequency in co-incident oroverlapping geographic areas has led to the development of extensioncarriers (which are not backwards compatible with legacy devices).Extension carriers may be used as a tool for carrier aggregation basedHetNet operation and improved spectral efficiency. A multi-carriercapable base station is able to operate at least one of its carriers asan extension carrier, on which a control channel (e.g. a channelcarrying resource scheduling information such as the Physical DownlinkControl Channel (PDCCH)), a Common reference Signal (CRS) (sometimesreferred to as a Cell-specific Reference Signal), and other informationcannot be transmitted. More specifically, an extension carrier may notbe used for transmission of any of the following:

-   -   a Physical Downlink Control Channel (PDCCH);    -   a Physical Hybrid ARQ Indicator Channel (PHICH);    -   a Physical Control Format Indicator Channel (PCFICH);    -   a Physical Broadcast Channel (PBCH);    -   a Primary Synchronization Signal (PSS);    -   a Secondary Synchronization Signal (SSS); or    -   a Common Reference Signal/Cell-specific Reference Signal (CRS).

An extension carrier therefore comprises a carrier that cannot beoperated as a single carrier (stand-alone) carrier, but must be a partof a component carrier set where at least one of the carriers in the setis a stand-alone-capable carrier, which can be used to transmit thescheduling information (and other control information) for the extensioncarrier.

Thus, when a first base station is operating a component carrier as anextension carrier, another base station may operate a component carrierof the same frequency to transmit a control channel, a CRS and othersuch information more reliably, in the same general geographic area asthe first base station, without significant interference because thereis no corresponding control channel, CRS and other such information onthe extension carrier operated by the first base station.

However, in communication systems in which extension carriers areemployed, the cross-carrier scheduling from the stand-alone (legacy)component carrier can cause an increase in control channel (PDCCH)blocking and control channel (PDCCH) capacity can become a limitingfactor of system performance. This is because of the additional controlchannel signalling required to schedule resources on multiple componentcarriers.

DISCLOSURE OF INVENTION

The invention therefore aims to provide a mobile communication system, amobile communication device, a communication node and associated methodswhich overcomes or at least mitigates the above issues.

According to one aspect of the present invention, there is providedcommunication apparatus for communicating with a plurality of mobilecommunication devices in a cellular communication system thecommunication apparatus comprising: means for operating at least onecommunication cell; means for communicating a plurality of subframeswith each of a plurality of communication devices within the at leastone cell, wherein: each sub-frame comprises a plurality of communicationresources defining a control region for communicating a respectivecontrol channel and a plurality of communication resources defining adata region for communicating a respective data channel; and thecommunicating means is operable to communicate: a first control channelhaving a first reference signal pattern (which may also referred to as a‘sequence’) in a control region of a first of the subframes; and asecond control channel having a second reference signal pattern(sequence) in a control region of a second of the subframes, wherein thesecond reference signal pattern (sequence) is different from the firstreference signal pattern (sequence).

The means for operating at least one communication cell may be operableto operate a first cell using a first component carrier and a secondcell using a second component carrier, and the first subframe may beprovided using the first component carrier and the second subframe maybe provided using the second component carrier.

The second component carrier may be operated as an extension carrier.The first component carrier may be operated as a stand-alone carrier.The communicating means may be operable to focus the second controlchannel spatially in a direction of a specific communication device.

The communicating means may be operable to transmit the first controlchannel omnidirectionally throughout the at least one cell.

The communication apparatus may further comprise means for determiningwhether a specific communication device should receive a first controlchannel having the first reference signal pattern, or a second controlchannel having the second reference signal pattern.

The determining means may be operable to determine whether the specificcommunication device should receive the first control channel having thefirst reference signal pattern, or the second control channel having thesecond reference signal pattern, based on a location of thecommunication device.

The determining means determining means may be operable to determinewhether the specific communication device should receive the firstcontrol channel having the first reference signal pattern, or the secondcontrol channel having the second reference signal pattern, based on thelocation of the communication device relative to further communicationapparatus.

The determining means may be operable to determine the location of thecommunication device relative to the further communication apparatusbased on a result of a measurement of a parameter representing adistance of the communication device from the further communicationapparatus.

The parameter representing a distance of the communication device fromthe further communication apparatus may comprise a reference signalreceived power (RSRP) of a signal transmitted by the furthercommunication apparatus.

The determining means may be operable to determine that the specificcommunication device should receive the first control channel having thefirst reference signal pattern if a predefined message has been receivedfrom the specific communication device.

The determining means may be operable to determine that the specificcommunication device should receive the second control channel havingthe second reference signal pattern if a further predefined message hasbeen received from the specific communication device.

The determining means may be operable to determine whether the specificcommunication device should receive a the first control channel havingthe first reference signal pattern, or the second control channel havingthe second reference signal pattern, in dependence on a measurementreport received from the specific communication device.

The communication apparatus may comprise a plurality of distributedantennas.

The communicating means may be operable to communicate the first controlchannel having a first reference signal pattern using any of theplurality of antennas.

The communicating means may be operable to communicate the secondcontrol channel having a second reference signal pattern using a subsetcomprising at least one, but not all, of the plurality of antennas.

The communicating means may be operable to communicate a control channelhaving a third reference signal pattern in a third of the subframesusing a subset comprising at least one, but not all, of the plurality ofantennas, wherein the third reference signal pattern may be differentfrom first reference signal pattern and the second reference signalpattern.

The communicating means may be operable to communicate radio framescomprising a plurality of subfames, each subframe having a differentrespective subframe location, and wherein the communicating means may beoperable: to communicate the first control channel having a firstreference signal pattern in a subframe at a subframe location, within aradio frame, selected from a first set of subframe location(s)comprising at least one subframe location; and may be operable tocommunicate the second control channel having a second reference signalpattern in a subframe at a subframe location, within a radio frame,selected from a second set of subframe location(s) comprising at leastone subframe location; wherein the first set of subframe location(s) maynot comprise the same subframe location(s) as the second set of subframelocation(s).

The first control channel having a first reference signal pattern maynot be communicated in a subframe at a subframe location of amulti-media broadcast over a single frequency network (MBSFN) subframeand/or may not be communicated in a subframe at a subframe location ofan almost blank subframe (ABS).

The second control channel having a second reference signal pattern maybe communicated in a subframe at a subframe location of a multi-mediabroadcast over a single frequency network (MBSFN). The second controlchannel having a second reference signal pattern may be communicated ina subframe of an almost blank subframe (ABS).

Control information communicated using the first and/or the second mayrepresent a resource allocation for a communication device. Eachreference signal pattern may comprise a demodulation reference signalpattern ‘DMRS’.

According to one aspect of the present invention, there is provided acommunication device for communicating with communication apparatus of acellular communication system said communication device comprising:means for registering said communication device in at least onecommunication cell operated by said communication apparatus; means forreceiving a plurality of sub-frames from said communication apparatus,wherein: each sub-frame comprises a plurality of communication resourcesdefining a control region for communicating a respective control channeland a plurality of communication resources defining a data region forcommunicating a respective data channel; and said receiving means isoperable: to receive a first control channel having a first referencesignal pattern in a control region of a first of said subframes; and toreceive a second control channel having a second reference signalpattern in a in a control region of a second of said subframes, whereinsaid second reference signal pattern may be different from said firstreference signal pattern; and means for interpreting control informationcommunicated in said first control channel having a first referencesignal pattern, and for interpreting control information communicated insaid second control channel having a second reference signal pattern.

The receiving means may be operable to receive the first subframe on afirst component carrier of a first frequency band and the secondsubframe on a the second component carrier of a second frequency band.The second component carrier may be operated as an extension carrier.The first component carrier may be operated as a stand-alone carrier.

The receiving means may be operable to receive the second controlchannel in a radio beam focussed spatially in a direction of thecommunication device.

The receiving means may be operable to receive the first control channelin a radio communication transmitted omnidirectionally throughout the atleast one cell.

The communication device may further comprise means for measuring aparameter representing a distance of the communication device fromfurther communication apparatus.

The parameter representing a distance of the communication device fromthe further communication apparatus may comprise a reference signalreceived power (RSRP) of a signal transmitted by the furthercommunication apparatus.

The communication device may further comprise means for transmitting apredefined message to the communication apparatus operating the cell independence on a result of the measurement of the parameter representinga distance of the communication device from the further communicationapparatus.

The predefined message may comprise a measurement report including theresult of the measurement.

The predefined message may comprise information representing an identityof the further communication apparatus and/or of a cell operated by thefurther communication apparatus.

The communication device may further comprise means for comparing theparameter against a predetermined threshold value.

The transmitting means may be operable to transmit the predefinedmessage if the comparison indicates that the parameter has risen abovethe threshold value.

The transmitting means may be operable to transmit a further predefinedmessage if the comparison indicates that the parameter has fallen belowthe threshold value.

The receiving means may be operable to receive radio frames comprising aplurality of subfames, each subframe having a different respectivesubframe location within the radio frame, and wherein the receivingmeans may be operable: to receive a first control channel having a firstreference signal pattern in a subframe at a subframe location, within aradio frame, selected from a first set of subframe location(s)comprising at least one subframe location; and may be operable toreceive a second control channel having a second reference signalpattern in a subframe at a subframe location, within a radio frame,selected from a second set of subframe location(s) comprising at leastone subframe location; wherein the first set of subframe location(s) maynot comprise the same subframe location(s) as the second set of subframelocation(s).

The first control channel having a first reference signal pattern maynot be received in a subframe at a subframe location of a multi-mediabroadcast over a single frequency network (MBSFN) and/or may not bereceived in a subframe at a subframe location of an almost blanksubframe (ABS). The second control channel having a second referencesignal pattern may be received in a subframe at a subframe location of amulti-media broadcast over a single frequency network (MBSFN). Thesecond control channel having a second reference signal pattern may bereceived in a subframe of an almost blank subframe (ABS).

The control information communicated using the first and/or the secondmay represent a resource allocation for the communication device.

The reference signal pattern may comprise a demodulation referencesignal pattern ‘DMRS’.

According to one aspect of the present invention, there is provided amethod, performed by communication apparatus, of communicating with aplurality of mobile communication devices in a cellular communicationsystem the method comprising: operating at least one communication cell;communicating a plurality of subframes with each of a plurality ofcommunication devices within the at least one cell, wherein eachsub-frame comprises a plurality of communication resources defining acontrol region for communicating a respective control channel and aplurality of communication resources defining a data region forcommunicating a respective data channel; communicating controlinformation using a first control channel having a first referencesignal pattern in a control region of a first of the subframes; andcommunicating control information using a second control channel havinga second reference signal pattern in a control region of a second of thesubframes, wherein the second reference signal pattern is different fromthe first reference signal pattern.

According to one aspect of the present invention, there is provided amethod, performed by a communication device, of communicating withcommunication apparatus of a cellular communication system the method:

registering the communication device in at least one communication celloperated by the communication apparatus;

receiving a plurality of sub-frames from the communication apparatus,wherein each sub-frame comprises a plurality of communication resourcesdefining a control region for communicating a respective control channeland a plurality of communication resources defining a data region forcommunicating a respective data channel; receiving a first controlchannel having a first reference signal pattern in a control region of afirst of the subframes; interpreting control information communicated inthe first control channel having a first reference signal pattern;receiving a second control channel having a second reference signalpattern in a in a control region of a second of the subframes, whereinthe second reference signal pattern is different from the firstreference signal pattern; and interpreting control informationcommunicated in the second control channel having a second referencesignal pattern.

According to one aspect of the present invention, there is provided acomputer program product comprising instructions operable to program aprogrammable processor to implement communication apparatus or acommunication device according as recited above.

According to one aspect of the present invention, there is providedcommunication apparatus for communicating with a plurality of mobilecommunication devices in a cellular communication system thecommunication apparatus comprising: means for operating at least onecommunication cell; means for communicating a plurality of subframeswith each of a plurality of communication devices within the at leastone cell, wherein: each sub-frame comprises a plurality of communicationresources defining a control region for communicating a respectivecontrol channel and a plurality of communication resources defining adata region for communicating a respective data channel; and thecommunicating means may be operable to communicate: control informationusing a first control channel having a first reference signal pattern ina control region of a first of the subframes; and control informationusing a second control channel having a second reference signal patternin one of the control and data regions of a second of the subframes,wherein the second reference signal pattern is different from the firstreference signal pattern.

According to one aspect of the present invention, there is provided acommunication device for communicating with communication apparatus of acellular communication system the communication device comprising: meansfor registering the communication device in at least one communicationcell operated by the communication apparatus; means for receiving aplurality of sub-frames from the communication apparatus, wherein: eachsub-frame comprises a plurality of communication resources defining acontrol region for communicating a respective control channel and aplurality of communication resources defining a data region forcommunicating a respective data channel; and the receiving means isoperable: to receive a first control channel having a first referencesignal pattern in a control region of a first of the subframes; and toreceive a second control channel having a second reference signalpattern in at least one of a control region and a data region of asecond of the subframes, wherein the second reference signal pattern maybe different from the first reference signal pattern; and means forinterpreting control information communicated in the first controlchannel having a first reference signal pattern, and for interpretingcontrol information communicated in the second control channel having asecond reference signal pattern.

According to one aspect of the present invention, there is provided acommunication apparatus for communicating with a plurality of mobilecommunication devices in a cellular communication system thecommunication apparatus comprising: means for operating at least onecommunication cell; means for communicating a plurality of subframeswith each of a plurality of communication devices within the at leastone cell, wherein: the communicating means is operable to communicate:control information using a first control channel omnidirectionallythroughout the cell; and control information using a second controlchannel in a direction spatially focussed towards a communication devicefor which the control information is intended.

According to one aspect of the present invention, there is provided acommunication device for communicating with communication apparatus of acellular communication system the communication device comprising: meansfor registering the communication device in at least one communicationcell operated by the communication apparatus; means for receiving aplurality of sub-frames from the communication apparatus, wherein: thereceiving means may be operable: to receive a first control channelomnidirectionally by the communication apparatus throughout the cell;and to receive a second control channel transmitted in a directionspatially focussed towards the communication device; and means forinterpreting control information communicated in the first controlchannel, and for interpreting control information communicated in thesecond control channel.

According to one aspect of the present invention, there is providedcommunication apparatus for communicating with a plurality of mobilecommunication devices in a cellular communication system thecommunication apparatus comprising: a cell controller adapted to operateat least one communication cell; a transceiver operable to communicate aplurality of subframes with each of a plurality of communication deviceswithin the at least one cell, wherein: each sub-frame comprises aplurality of communication resources defining a control region forcommunicating a respective control channel and a plurality ofcommunication resources defining a data region for communicating arespective data channel; and the transceiver is may be further operableto communicate: control information using a first control channel havinga first reference signal pattern in a control region of a first of thesubframes; and control information using a second control channel havinga second reference signal pattern in at least one of the control anddata regions of a second of the subframes, wherein the second referencesignal pattern is different from the first reference signal pattern.

According to one aspect of the present invention, there is provided acommunication device for communicating with communication apparatus of acellular communication system the communication device comprising: acell registration module operable to register the communication devicein at least one communication cell operated by the communicationapparatus; a transceiver operable to receive a plurality of sub-framesfrom the communication apparatus, wherein: each sub-frame comprises aplurality of communication resources defining a control region forcommunicating a respective control channel and a plurality ofcommunication resources defining a data region for communicating arespective data channel; and the transceiver is further operable: toreceive a first control channel having a first reference signal patternin a control region of a first of the subframes; and to receive a secondcontrol channel having a second reference signal pattern in at least oneof the control region and the data region of a second of the subframes,wherein the second reference signal pattern is different from the firstreference signal pattern; and a processor operable to interpret controlinformation communicated in the first control channel having a firstreference signal pattern, and to interpret control informationcommunicated in the second control channel having a second referencesignal pattern.

Aspects of the invention extend to computer program products such ascomputer readable storage media having instructions stored thereon whichare operable to program a programmable processor to carry out a methodas described in the aspects and possibilities set out above or recitedin the claims and/or to program a suitably adapted computer to providethe apparatus recited in any of the claims.

Each feature disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently (or in combination with) any other disclosedand/or illustrated features. In particular but without limitation thefeatures of any of the claims dependent from a particular independentclaim may be introduced into that independent claim in any combinationor individually.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the attached figures in which:

FIG. 1 schematically illustrates a telecommunication system;

FIG. 2 illustrates a possible subframe configuration for componentcarriers for the telecommunication system of FIG. 1;

FIG. 3 shows a simplified illustration of a resource grid fordemodulation reference signals in the telecommunication system of FIG.1;

FIG. 4 shows a simplified block diagram of a first base station for thetelecommunication system of FIG. 1;

FIG. 5 shows a simplified block diagram of a second base station for thetelecommunication system of FIG. 1;

FIG. 6 shows a simplified block diagram of a mobile communication devicefor the telecommunication system of FIG. 1;

FIG. 7 shows a simplified flow chart illustrating operation of thetelecommunication system of FIG. 1;

FIG. 8 schematically illustrates another telecommunication system;

FIG. 9 illustrates a possible subframe configuration for componentcarriers for the telecommunication system of FIG. 8;

FIG. 10 illustrates another possible subframe configuration forcomponent carriers for the telecommunication system of FIG. 8;

FIG. 11 schematically illustrates another telecommunication system;

FIG. 12 illustrates a possible subframe configuration for componentcarriers for the telecommunication system of FIG. 10;

FIG. 13 schematically illustrates another telecommunication system;

FIG. 14 illustrates a radio frame for the telecommunication system ofFIG. 13;

FIG. 15 illustrates a number of possible subframe configurations forcomponent carriers for the telecommunication system of FIG. 13;

FIG. 16 schematically illustrates another telecommunication system; and

FIG. 17 illustrates a number of possible subframe configurations forcomponent carriers for the telecommunication system of FIG. 16.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which a user of any of a plurality of mobile communicationdevices 3-1 to 3-7 can communicate with other users via one or more of aplurality of base stations 5-1, 5-2 and 5-3. In the system illustratedin FIG. 1, each base station 5 shown is an Evolved Universal TerrestrialRadio Access Network (E-UTRAN) base station capable of operating in amulti-carrier environment.

In FIG. 1, the base station labelled 5-1 comprises a so called ‘macro’base station operating a plurality of relatively geographically large‘macro’ cells 7, 8 using respective component carriers (CCs) C1, C2, ofa component carrier set. In this embodiment, the macro base station 5-1operates component carrier C1 as a primary component carrier on which aprimary cell (PCell) 7 is provided, and component carrier C2 as asecondary component carrier on which a secondary cell (SCell) 8 isprovided. The PCell 7 has a larger geographical coverage than the SCell8. The difference in the size of the PCell 7 and SCell 8 may be bydesign (e.g. as a result of using a lower transmit power for componentcarrier C2) or may result from one or more radio environmental factorsaffecting the primary carrier C1 and secondary carrier C2 to differentextents (e.g. path loss affecting a lower frequency primary carrier C1to a lesser extent than a higher frequency secondary carrier C2).

The other base stations 5-2, 5-3 shown in FIG. 1 each comprises a socalled ‘pico’ base station operating a plurality of ‘pico’ cells 9-2,9-3, 10-2, 10-3, using a component carrier set having component carriers(CCs) C1, C2 corresponding in frequency to those used by the macro-basestation 5-1. Each pico base station 5-2, 5-3 operates a respective picoprimary cell (PCell) 9-2, 9-3 on component carrier C2 and a respectivepico secondary cell (SCell) 10-2, 10-3 on component carrier C1. Thus,the pico Pcells 9 share substantially the same frequency band as themacro Scell 8, and the pico Scells 10 share substantially the samefrequency band as the macro Pcell 7. As seen in FIG. 1, the power of thecarriers C1, C2 used to provide the pico cells 9, 10 is set such thatthe geographical coverage of the pico PCells 9, of this example, aresubstantially co-incident with the geographical coverage of the picoSCells 10.

The power used to provide pico cells 9, 10 is low relative to the powerused for the macro cells 7, 8 and the pico cells 9, 10 are thereforesmall relative to the macro cells 7, 8. As shown in FIG. 1, in thisexample the geographical coverage of each of the pico cells 9, 10 fallscompletely within the geographical coverage of the macro PCell 7 andoverlaps partially with the geographical coverage of the macro SCell 8.

Referring to FIG. 2, in which the subframe configuration for thecomponent carriers for each of the cells is illustrated, it will beapparent that there is a potential for relatively high communicationinterference between the macro PCell 7 and each of the pico SCells 10.The risk of interference is high because the macro PCell 7 and picoSCells 10 operate in co-incident geographical regions and use a commoncomponent carrier frequency. Further, the strength of communicationsignals from the macro base station 5-1, in the geographical areacovered by each pico Scell 10, may be comparable to communicationsignals from the respective pico base station 5-2, 5-3 because of therelatively high power used by the macro base station 5-1 compared tothat used by the pico base stations 5-2, 5-3. Whilst there is also thepotential for some interference between the macro SCell 8 and each ofthe pico PCells 9, any such interference is likely to be relativelysmall and restricted to the relatively small geographical region inwhich the macro SCell 8 and pico PCells 9 overlap.

In order to alleviate the issue of interference, the component carrierC2 used for the macro Scell 8 is operated by the macro base station 5-1as an extension carrier on which the nature of information that may betransmitted is restricted. Specifically, the component carrier, whenoperating as the extension carrier may not be used for transmission ofany of the following: [0089] a Physical Downlink Control Channel(PDCCH); [0090] a Physical Hybrid ARQ Indicator Channel (PHICH); [0091]a Physical Control Format Indicator Channel (PCFICH); [0092] a PhysicalBroadcast Channel (PBCH); [0093] a Primary Synchronization Signal (PSS);[0094] a Secondary Synchronization Signal (SSS); or [0095] a CommonReference Signal/Cell-specific Reference Signal (CRS).

The macro base station 5-1 operates carrier C1 for the PCell 7 as astand-alone carrier having a Physical Downlink Control Channel (PDCCH),which can be used to schedule the resources of its own component carrierC1 (as shown by arrow X). The PDCCH of component carrier C1 can also beused to schedule the resources of component carrier C2 (‘cross carrierscheduling’) to be used for communication purposes by a mobilecommunication device 3 when operating in the macro Scell 8 (as shown byarrow Y). The PDCCH is transmitted omnidirectionally throughout thecell.

The respective component carrier C1 used for each of the pico SCells 10is also operated as an extension carrier by the associated pico basestation 5-2, 5-3. The respective component carrier C2 used for each ofthe pico Pcells 9 is operated, by the associated pico base station 5-2,5-3, as a stand-alone carrier having an associated PDCCH for schedulingresources within its own component carrier C2 (as shown by arrow X′).This PDCCH can also be used for cross carrier scheduling resources ofcomponent carrier C1 to be used for communication purposes by a mobilecommunication device 3 when operating in the associated pico Scell 10(as shown by arrow Y′).

As illustrated in FIGS. 1 and 2, in this embodiment whilst aconventional PDCCH is not provided on the extension carriers, adedicated Beamformed Physical Downlink Control Channel (BFed PDCCH) 4-1,4-2, 4-5 is provided using the extension component carrier C2 of themacro SCell 8. The BFed PDCCH 4-1, 4-2, 4-5 is directional and can beused selectively to schedule resources of the extension componentcarrier C2 for the macro SCell 8 (as shown by arrow Z) for specificmobile communication devices 3. The BFed PDCCH is used in conjunctionwith frequency selective scheduling in which the mobile communicationdevice reports the channel state information (CSI) such as channelquality indicator (CQI) for each resource block (RB) or group of RBs infrequency domain of the system bandwidth and the base station selectsthe best resource blocks to use to schedule the BFed PDCCH for eachterminal.

In this exemplary embodiment, a BFed PDCCH is not provided for theextension component carrier C1 of the pico SCells 10-2, 10-3. Insteadeach pico base station 5-2, 5-3 operates its respective extensioncomponent carrier C1 as a completely PDCCH-less component carrier asshown in FIG. 2.

The PDCCH of the primary component carrier C1, operated by the macrobase station 5-1, can thus be used for scheduling resources (e.g. asshown by arrow Y) for a mobile communication device 3-7, located in themacro SCell 8, but which is in geographical close proximity to a picoPCell 9-2 being operated on the same component carrier C2 as the macroSCell 8. Accordingly, interference between the macro SCell 8 and thepico PCell 9-2 is avoided because, although the macro SCell 8 and thepico PCell 9-2 are being operated using same component carrier frequencyband (C2), the control information for each cell is transmitted using adifferent respective component carrier frequency band.

The BFed PDCCH 4-1, 4-2, 4-5 of the extension component carrier C2 formacro SCell 8 can be used selectively to schedule resources for arespective mobile communication device 3-1, 3-2, 3-5, operating withinthe macro SCell 8, but which is not geographically close to one of thepico PCells 9-2, 9-3. Accordingly, where interference is not such asignificant risk, the capacity of the PDCCH of the component carrier C1used for the macro Pcell 7 can, beneficially, be conserved withoutsignificantly affecting interference.

For the smaller pico cells in which control channel capacity is not suchan issue, the PDCCH of the respective component carrier C2 operated byeach pico base station 5-2, 5-3, can be used for the cross carrierscheduling of resources for any mobile communication device 3-3, 3-4located in the respective pico SCell 10-2, 10-3. As described above, thepico cells are geographically located entirely within the region coveredby the macro PCell 7. Accordingly, the absence of a BFed PDCCH, for thecomponent carrier C1 operated by each pico base station 5-2, 5-3, avoidsthe interference that could otherwise potentially result with the PDCCHof the macro PCell's component carrier C1.

Beamformed Physical Downlink Control Channel (BFed PDCCH)

A possible implementation of a BFed PDCCH will now be described, in moredetail.

The beamforming of the BFed PDCCH 4-1, 4-2, 4-5 is achieved using amulti-layer beamforming approach that is suitable for a multiple inputmultiple output (MIMO) based communication system in which thetransmitters and the receivers of the signals have multiple antennas.Beamforming is achieved using a precoding technique in which the phase(and possibly gain) of each stream of signals transmitted from each of aplurality of antennas is independently weighted such that the power ofeach signal stream is focussed in the direction of interest (e.g. thatof the mobile communication device for which the BFed PDCCH is intended)to maximise the signal level. Similarly, the power of each stream ofsignals is minimised in other directions, including directions in whichinterference is a potential issue (e.g. that of the pico cells 9, 10).

In order to beamform successfully, the state of the channel is analysedbased on Channel State Information (CSI) measured by the mobilecommunication devices 3 and reported to the macro base station 5-1. TheCSI comprises information such as a rank indicator (RI), precodingmatrix indicator (PMI), a channel quality indicator (CQI) and/or thelike. Based on this information, an appropriate type of beamforming isselected. For example, where full CSI is reliably available astatistical eigenvector beamforming technique may be used. In situationswhere a more limited CSI is available, an interpolation technique may beused estimate the CSI for beamforming. In situations where no CSI isavailable the CSI may be estimated blindly at the base station, forexample from received signal statistics or uplink signals received fromthe terminal.

FIG. 3 shows a resource grid for an orthogonal frequency divisionmultiplexing (OFDM) subframe 30 for the communication system 1 of FIG.1, in which a BFed PDCCH is provided. The resource grid shown is for aresource block (RB) pair each RB having, for example, a resource gridsimilar to that described in section 6.2 of the 3^(rd) GenerationPartnership Project (3GPP) Technical Standard (TS) 36.211 V10.2.0 andshown in FIG. 6.2.2-1 of that standard.

As seen in FIG. 3, the BFed PDCCH transmission is provided in a set ofresource elements 35 in a control region 31 of the subframe 30. Thecontrol region 31 comprises resource elements 35 of the first three OFDMsymbols of the first slot of the subframe 30, and spans all twelvesubcarrier frequencies of one resource block (RB). The remainingresource elements 35 of the first slot and the resource elements 35 ofthe second slot form a data region 33 in which the Physical DownlinkShared Channel (PDSCH) is transmitted. A set of UE specific PDSCHdemodulation reference signals (DMRS) and UE specific BFed PDCCH DMRSare provided in the data region 33 and control region 31 respectively asillustrated.

The DMRS pattern for the BFed PDCCH is different to that used for alegacy PDCCH. In the DMRS pattern shown in FIG. 3, PDSCH DMRS forantenna ports 7 and 8 are transmitted in resource elements 35 at threeevenly distributed subcarrier frequencies, in each of the last twosymbols of the first slot and in each of the last two symbols of thesecond slot. PDSCH DMRS for antenna ports 9 and 10 are also transmittedin resource elements 35 at three evenly distributed subcarrierfrequencies (different to those used for ports 7 and 8), in each of thelast two symbols of the first slot and in each of the last two symbolsof the second slot. BFed PDCCH DMRS for antenna ports x1 and x2 aretransmitted in resource elements 35 at three evenly distributedsubcarrier frequencies, in each of the first two symbols of the firstslot. BFed PDCCH DMRS for antenna ports x3 and x4 are transmitted inresource elements 35 at three evenly distributed subcarrier frequencies(different to those used for ports x3 and x4), in each of the first twosymbols of the first slot.

Macro Base Station

FIG. 4 is a block diagram illustrating the main components of the macrobase station 5-1 shown in FIG. 1. The macro base station 5-1 comprisesan E-UTRAN multi-carrier capable base station comprising a transceivercircuit 431 which is operable to transmit signals to, and to receivesignals from, the mobile communication devices 3 via a plurality ofantennas 433. The base station 5-1 is also operable to transmit signalsto and to receive signals from a core network via a network interface435. The operation of the transceiver circuit 431 is controlled by acontroller 437 in accordance with software stored in memory 439.

The software includes, among other things, an operating system 441, acommunication control module 442, a component carrier management module443, a measurement management module 445, a control channel managementmodule 446, a direction determination module 447, a resource schedulingmodule 448, and a beamforming module 449.

The communication control module 442 is operable to controlcommunication with the mobile communication devices 3 on the componentcarriers (CCs) C1, C2, of its component carrier set. The componentcarrier management module 443 is operable to manage the use of thecomponent carriers C1, C2 and, in particular, the configuration andoperation of the macro PCell 7 and macro SCell 8 and the operation ofthe secondary component carrier C2 for the SCell 8 as an extensioncarrier. The measurement management module 445 communicates with themobile communication device 3 to configure the mobile communicationdevice 3 to initiate measurement of the CSI and to receive and analysemeasurement reports received from the mobile communication devices 3 toassess the channel state for the purposes of beamforming. The directiondetermination module 447 determines the directional position of a mobilecommunication device 3, relative to the base station 5-1, forbeamforming purposes, from the uplink signals that the base station 5-1receives from that mobile communication device 3. The resourcescheduling module 448 is responsible for scheduling the resources of theprimary and extension component carrier C1, C2 to be used by the mobilecommunication devices 3 operating in the macro cells 7, 8. Thebeamforming module 449 manages the formation of the directional ‘beam’via which the BFed PDCCH 4-1, 4-2, 4-5 is provided to the respectivemobile communication devices 3-1, 3-2, 3-5.

In this exemplary embodiment, the control channel management module 446determines which control channel to use for scheduling resources of theextension carrier C2 of the macro SCell 8 based on trigger messagesreceived from the mobile communication device 3. These trigger messagesindicate either that a mobile communication device is within range of apico base station 5-2, 5-3 or that a mobile communication device 3 is nolonger within range of a pico base station 5-2, 5-3.

Specifically, if a mobile communication device 3 has not issued atrigger message indicating that it is within range of a pico basestation 5-2, 5-3, or if it has issued a trigger message indicating thatit is no longer within range of a pico base station 5-2, 5-3, then thecontrol channel management module 446 determines that the mobilecommunication device 3 should receive resource scheduling for theextension carrier C2 of the macro SCell 8 via a BFed PDCCH provided onthe extension carrier C2.

If a mobile communication device 3 has issued a trigger messageindicating that it is within range of a pico base station 5-2, 5-3, thenthe control channel management module 446 determines that the mobilecommunication device 3 should receive resource scheduling for theextension carrier C2 of the macro SCell 8 via a PDCCH provided on theprimary component carrier C1 of the macro PCell 7.

In the above description, the base station 5-1 is described for ease ofunderstanding as having a number of discrete modules. Whilst thesemodules may be provided in this way for certain applications, forexample where an existing system has been modified to implement theinvention, in other applications, for example in systems designed withthe inventive features in mind from the outset, these modules may bebuilt into the overall operating system or code and so these modules maynot be discernible as discrete entities.

Pico Base Station

FIG. 5 is a block diagram illustrating the main components of a picobase station 5-2, 5-3 shown in FIG. 1. Each pico base station 5-2, 5-3comprises an E-UTRAN multi-carrier capable base station comprising atransceiver circuit 531 which is operable to transmit signals to, and toreceive signals from, the mobile communication devices 3 via at leastone antenna 533.

The base station 5-2, 5-3 is also operable to transmit signals to and toreceive signals from a core network via a network interface 535. Theoperation of the transceiver circuit 531 is controlled by a controller537 in accordance with software stored in memory 539.

The software includes, among other things, an operating system 541, acommunication control module 542, a component carrier management module543, a cell type identifier module 547 and a resource scheduling module548.

The communication control module 542 is operable to controlcommunication with the mobile communication devices 3 on the componentcarriers (CCs) C1, C2, of its component carrier set. The componentcarrier management module 543 is operable to manage the use of thecomponent carriers C1, C2 and in particular the configuration andoperation of the pico PCell 9 and pico SCell 10 and the operation of thesecondary component carrier C1 for the SCell 10 as an extension carrier.The cell type identifier module 547 provides information for identifyingthe cells controlled by the base station 5-2, 5-3 as pico cells 9, 10.This information is provided to mobile communication devices 3 that comewithin (or close to) the coverage area of the pico Pcell 9. In thisexemplary embodiment, for example, the cell type identifier module 547broadcasts information identifying the cells it controls to be picocells. The resource scheduling module 548 is responsible for schedulingthe resources of the primary and extension component carrier C2, C1 tobe used by the mobile communication devices 3 operating in the picocells 9, 10.

In the above description, the base station 5-2, 5-3 is described forease of understanding as having a number of discrete modules. Whilstthese modules may be provided in this way for certain applications, forexample where an existing system has been modified to implement theinvention, in other applications, for example in systems designed withthe inventive features in mind from the outset, these modules may bebuilt into the overall operating system or code and so these modules maynot be discernible as discrete entities.

Mobile Communication Device

FIG. 6 is a block diagram illustrating the main components of the mobilecommunication devices 3 shown in FIG. 1. Each mobile communicationdevice 3 comprises a mobile (or ‘cell’ telephone) capable of operatingin a multi-carrier environment. The mobile communication device 3comprises a transceiver circuit 651 which is operable to transmitsignals to, and to receive signals from, the base stations 5 via atleast one antenna 653. The operation of the transceiver circuit 651 iscontrolled by a controller 657 in accordance with software stored inmemory 659.

The software includes, among other things, an operating system 661, acommunication control module 662, a measurement module 665, and a cellidentification module 667, a cell proximity detection module 668, and aresource determination module 669.

The communication control module 662 is operable for managingcommunication with the base stations 5 on the associated componentcarriers (CCs) C1, C2. The measurement module 665 receives measurementconfiguration information from the base station 5-1 for the purposes ofconfiguring the mobile communication device 3 to take measurements ofthe CSI. The measurement module 665 manages performance of themeasurements of CSI (e.g. for the macro cells 7, 8), generatesassociated measurement reports and transmits the generated reports tothe macro base station 5-1. The measurement module 665 also determinesreference signal received power (RSRP) for the pico cells 9, 10 for usein determining the proximity of the mobile communication device 3 to thepico cells. The cell identification module 667 is operable to determinethe type of cell, which the mobile communication device 3 enters, orcomes geographically close to, from information provided by the basestation 5-2, 5-3, controlling that cell. In this exemplary embodiment,for example, the cell identification module 667 is operable to receivethe information for identifying the cell type that is broadcast by apico base station 5-2, 5-3, and to identify the cell type to be a picocell from the received information.

The cell proximity detection module 668 uses the measurements of RSRPfrom the pico Pcells 9 to determine the proximity of the mobilecommunication device 3 to the pico Pcells 9 by comparing the RSRPmeasurement to a predetermined ‘trigger’ threshold 663. The triggerthreshold is set such that an RSRP above the trigger threshold indicatesthat the mobile communication device 3 is in a geographical locationthat is close enough to a pico Pcell 9 for there to be a risk ofassociated control channel interference between the PDCCH on the primarycarrier (C2) of the pico PCell 9 and the BFed PDCCH on the extensioncarrier C2 of the macro SCell 8

Hence, if the RSRP measurement exceeds the threshold value, then themobile communication device 3 is deemed to be sufficiently close to (orwithin) the pico cell for there to be a risk of interference between anyBFed PDCCH transmitted on the extension carrier C2 of the macro SCell 8with the PDCCH of transmitted on the extension carrier C2 of the picoPCell 9. When the trigger threshold 663 is exceeded, the cell proximitydetection module 668 triggers a message to the macro base station 5-1indicating that the mobile communication device is within range of apico base station 5-2, 5-3. When the RSRP measurement drops below thetrigger threshold 663, the cell proximity detection module 668 triggersa message to the macro base station 5-1 indicating that the mobilecommunication device is no longer within range of a pico base station5-2, 5-3.

The resource determination module 669 determines the resources scheduledfor use by the mobile communication devices 3 for communication purposesby decoding the PDCCH and/or BFed PDCCH appropriately.

In the above description, the mobile communication device 3 is describedfor ease of understanding as having a number of discrete modules. Whilstthese modules may be provided in this way for certain applications, forexample where an existing system has been modified to implement theinvention, in other applications, for example in systems designed withthe inventive features in mind from the outset, these modules may bebuilt into the overall operating system or code and so these modules maynot be discernible as discrete entities.

Operation

FIG. 7 is a flow chart illustrating typical operation of thecommunication system 1 to schedule resources for use by a mobilecommunication device (MCD) 3 during communications.

In FIG. 7, the exemplary operation scenario begins (at S1) when a mobilecommunication device 3 starts operating in the Scell 8 of the macro basestation 5-1, in a geographical location that is sufficiently far fromthe pico Pcells 9 for there to be little risk of associated controlchannel to control channel interference. The base station 5-1 determinesthe direction of the mobile communication device 3 relative to the basestation at S2 and identifies an appropriate precoding matrix (alsoreferred to as a precoding vector) for use in beamforming the BFed PDCCHfor that mobile communication device 3 in the determined direction. Themacro base station 5-1 schedules the resources for the extension carrierC2 of the macro SCell 8 using within-carrier scheduling via the BFedPDCCH (at S3).

In this example, each pico base station broadcasts information foridentifying itself to be a pico base station 5-2, 5-3 at S4 and themobile communication device 3 determines, from this broadcast identityinformation, that the base station 5-2, 5-3 is a pico base station (atS5). The mobile communication device 3 identifies the reference signalsthat it receives from the pico base stations 5-2, 5-3 and then monitorsthe reference signal received power (RSRP) of these reference signalsrelative to the predetermined trigger threshold (at S6).

In this example, while the RSRP remains below the trigger threshold, theprocess in steps S2 to S6 is repeated via loop L1. When the RSRPincreases above the trigger threshold it sends a ‘trigger’ message tothe macro base station 5-1 to indicate that it is in sufficient range ofa pico base station 5-2, 5-3, for control channel interference to be asignificant risk at S7. On receipt of the trigger message, the macrobase station 5-1 determines that it should no longer use a BFed PDCCHfor that mobile communication device 3 and schedules the resources forthe extension carrier C2 of the macro SCell 8 using cross-carrierscheduling via the PDCCH of the macro PCell's primary component carrierC1 at S8.

The mobile communication device 3 continues to monitor the referencesignal received power (RSRP) of the reference signals from the pico basestation 5-3, 5-3 relative to the predetermined trigger threshold at S6(via loop L2). While the RSRP remains above the trigger threshold, theprocess in step S8 is repeated via loop L4. When the RSRP drops belowthe trigger threshold it sends another ‘trigger’ message to the macrobase station 5-1 to indicate that it is no longer in sufficient range ofa pico base station 5-2, 5-3 for control channel interference to be asignificant risk (at S9 via loop IA). On receipt of the further triggermessage, the macro base station 5-1 determines that it can start to usea BFed PDCCH for that mobile communication device 3 again and schedulesthe resources for the extension carrier C2 of the macro SCell 8 usingwithin-carrier scheduling via the BFed PDCCH of the macro SCell'sextension component carrier C2 (at S3) following appropriate directionfinding and beamforming (at S2).

Application in a Communication System in which Macro PCell and PicoPCell Use

Same Carrier

FIG. 8 schematically illustrates a further mobile (cellular)telecommunication system 81. The telecommunication system 81 is similarto that of FIG. 1 and corresponding parts are given the same referencenumerals.

In the telecommunication system 81, a plurality of mobile communicationdevices 3-1 to 3-7 can communicate with other users via one or more of aplurality of base stations 5-1, 5-2 and 5-3. In the system illustratedin FIG. 1, each base station 5 shown is an Evolved Universal TerrestrialRadio Access Network (E-UTRAN) base station capable of operating in amulti-carrier environment.

In FIG. 8, the base station labelled 5-1 comprises a macro base stationoperating a plurality of relatively geographically large macro cells 7,8 using respective component carriers (CCs) C1, C2, of a componentcarrier set. In this embodiment, the macro base station 5-1 operatescomponent carrier C1 as a primary component carrier on which a primarycell (PCell) 7 is provided, and component carrier C2 as a secondarycomponent carrier on which a secondary cell (SCell) 8 is provided. ThePCell 7 has a larger geographical coverage than the SCell 8.

The other base stations 5-2, 5-3 shown in FIG. 8, each comprises a picobase station operating a plurality of ‘pico’ cells 9-2, 9-3, 10-2, 10-3,using a component carrier set having component carriers (CCs) C1, C2corresponding in frequency to those used by the macro-base station 5-1.In this exemplary embodiment, unlike that shown in FIG. 1, each picobase station 5-2, 5-3 operates a respective pico primary cell (PCell)9-2, 9-3 on component carrier C1 and a respective pico secondary cell(SCell) 10-2, 10-3 on component carrier C2.

Thus, unlike the system of FIG. 1, the pico Pcells 9 share substantiallythe same frequency band as the macro Pcell 7, and the pico Scells 10share substantially the same frequency band as the macro Scell 8. Thegeographical coverage of each of the pico cells 9, 10 falls completelywithin the geographical coverage of the macro PCell 7. However, theoverlap between the pico cells 9 and 10 and the macro SCell 8 isrelatively small.

Referring to FIG. 9, in which the subframe configuration for thecomponent carriers for each of the cells is illustrated, it will beapparent that there is a potential for relatively high communicationinterference between the PDCCH of the macro PCell 7 and the PDCCH ofeach of the pico PCells 9. In this exemplary embodiment, however, thisinterference is avoided by using a time domain solution in which themacro base station 5-1 transmits a PDCCH only in certain subframes andthe pico base stations 5-2, 5-3 transmits a PDCCH in other subframesthat do not overlap in time with the subframes used by the base station5-1.

More specifically, the macro base station 5-1 uses a first predeterminedset of subframes of a radio frame (in this example even numberedsubframes) to transmit a PDCCH and each pico base station 5-2, 5-3 usesa second predetermined set of subframes of a radio frame (in thisexample odd numbered subframes) to transmit a respective PDCCH.Accordingly, because the PDCCH provided by the macro base station 5-1and the pico base stations 5-2, 5-3, do not overlap the risk of controlchannel to control channel interference is avoided. The subframes inwhich a particular base station 5 does not transmit a PDCCH are also notused for data (e.g. PDCCH) transmission by that base station and,accordingly, are referred to as almost blank subframes (ABS). These ABSmay, however, be used for transmission of common/cell-specific referencesignals (CRS).

The Potential for any Interference Between the Macro SCell 8 and Each ofthe Pico SCells 10 is Relatively Small

Each base station 5 operates carrier C1 for its PCell 7, 9 as astand-alone carrier having a Physical Downlink Control Channel (PDCCH),which can be used to schedule the resources of its own component carrierC1 (as shown by arrows X and X′). The PDCCH of each component carrier C1can also be used to schedule the resources of component carrier C2(‘cross carrier scheduling’) to be used for communication purposes by amobile communication device 3 when operating in the corresponding Scell8, 10 (e.g. as shown by arrow Y).

The respective component carrier C2 used for each of the Scells 8, 10 isoperated, by the associated base station 5, as an extension carrier (asdescribed previously) on which a BFed PDCCH 4-1, 4-2, 4-3, 4-5, 4-8 canbe provided. The BFed PDCCH 4-1, 4-2, 4-3, 4-5, 4-8 is directional andcan be used selectively to schedule resources of the extension componentcarrier C2 for each SCell 8, 10 (e.g. as shown by arrows Z and Z′) forspecific mobile communication devices 3. The BFed PDCCH of eachextension component carrier C2 can also be used to schedule theresources of the related primary component carrier C1 (‘cross carrierscheduling’) to be used for communication purposes by a mobilecommunication device 3 when operating in the corresponding Pcell 7, 9(e.g. as shown by arrow W′).

The BFed PDCCH 4-1, 4-2, 4-3, 4-5, 4-8 of the extension componentcarrier C2 for each SCell 8, 10 can be used selectively to scheduleresources for a respective mobile communication device 3-1, 3-2, 3-3,3-5, 3-8 operating within in the corresponding SCell 8, 10. Accordingly,the risk of interference in the region in which the macro SCell 8 andpico SCell 10 does overlap is significantly reduced because of thegeographically localised nature of the BFed PDCCH. The DMRS pattern forthe BFed PDCCH is different to that used for a legacy PDCCH.

FIG. 10 shows another possible subframe configuration for the componentcarriers for the system of FIG. 8. In the configuration shown in FIG.10, the control region of the subframes provided using component carrierC2 used for each SCell 8, 10 is partitioned into a BFed PDCCH region inwhich the BFed PDCCH is provided, and a PDCCH-less region in which noPDCCH or BFed PDCCH is provided. The regions are generally equal sizedand are partitioned such that the BFed PDCCH region for the macro SCell8 does not overlap with the BFed PDCCH region for the pico SCell 10,thereby reducing the small risk of control channel to control channelinterference even further.

Application in a Communication System in which Only the Pico BaseStations Use a

BFed PDCCH

FIG. 11 schematically illustrates a further mobile (cellular)telecommunication system 111 and FIG. 12 shows a possible subframeconfiguration for the component carriers for the system of FIG. 11. Thetelecommunication system 111 is similar to that of FIG. 8 andcorresponding parts are given the same reference numerals.

The communication system is, essentially, the same as that shown in FIG.8 except that only the pico base stations 5-2, 5-3 provide a BFed PDCCHand, unlike the system of FIG. 8, the macro base station 5-1 providesall resource scheduling for the macro SCell 8 via a PDCCH provided inthe primary component carrier C1 for the macro PCell 7 (e.g. as shown byarrow Y in FIG. 12).

More specifically, each base station 5 operates carrier C1 for its PCell7, 9 as a stand-alone carrier having a PDCCH that can be used toschedule the resources of its own component carrier C1 (as shown byarrows X and X′). The PDCCH of each component carrier C1 can also beused to schedule the resources of component carrier C2 (‘cross carrierscheduling’) to be used for communication purposes by a mobilecommunication device 3 when operating in the corresponding Scell 8, 10(e.g. as shown by arrow Y).

The respective component carrier C2 used for each of the Scells 8, 10 isoperated, by the associated base station 5, as an extension carrier asdescribed previously. However, the component carrier C2 used for themacro Scell 8 is not provided with a PDCCH or a BFed PDCCH and so canonly be scheduled using the PDCCH provided on the primary componentcarrier C1. The component carrier C2 used for each pico Scell 10operated by the associated pico base station 5-2, 5-3 can be providedwith a BFed PDCCH 4-3, 4-8.

The BFed PDCCH 4-3, 4-8 is directional and can be used selectively toschedule resources of the extension component carrier C2 for each picoSCell 10 (e.g. as shown by arrow Z′) for specific mobile communicationdevices 3. The BFed PDCCH of the extension component carrier C2 for eachpico SCell 10 can also be used to schedule the resources of the relatedprimary component carrier C1 (‘cross carrier scheduling’) to be used forcommunication purposes by a mobile communication device 3 (e.g. as shownby arrow W′).

The BFed PDCCH 4-3, 4-8 of the extension component carrier C2 for eachpico SCell 10 can thus be used selectively to schedule resources for arespective mobile communication device 3-3, 3-8 operating within thecorresponding SCell 10. Accordingly, the risk of control channel tocontrol channel interference in the region in which the macro SCell 8and pico SCell 10 overlaps is significantly reduced.

Application in a Single Carrier Communication System

FIG. 13 schematically illustrates a further mobile (cellular)telecommunication system 131, FIG. 14 shows the configuration of a radioframe for the system 131 of FIG. 13, and FIG. 15 shows a number ofpossible subframe configurations for the system of FIG. 13. Thetelecommunication system 131 has similarities to those described earlierand corresponding parts are given the same reference numerals. In thesystem illustrated in FIG. 13, each base station 5 shown is an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) base stationcapable of operating in a single-carrier environment.

A major difference between the system 131 shown in FIG. 13 and thosedescribed earlier is that the telecommunication system 131 is a singlecomponent carrier system which has been adapted in a manner that allowslegacy mobile communication devices to use the system as normal (e.g.those defined by the 3^(rd) Generation Partnership Project (3GPP)release 8, 9 and 10 standards) whilst more advanced mobile communicationdevice can advantageously be scheduled using a BFed-PDCCH.

In FIG. 13, the base station labelled 5-1 comprises a macro base stationoperating a relatively geographically large macro cell 7 using a singlecomponent carrier C1 (e.g. a backwards compatible or ‘legacy’ componentcarrier). The other base stations 5-2, 5-3 shown in FIG. 13 eachcomprises a pico base station operating a pico cell 9-2, 9-3, using acomponent carrier C1 of the same frequency as the component carrier usedby the macro base station 5-1.

The power used to provide pico cells 9 is low relative to the power usedfor the macro cell 7 and the pico cells 9 are therefore small relativeto the macro cell 7. As shown in FIG. 13, in this example thegeographical coverage of each of the pico cells 9 falls completelywithin the geographical coverage of the macro cell 7.

Referring to FIG. 14, the configuration of a radio frame 140 for thecommunication system 113 is shown. As seen in FIG. 14, and as thoseskilled in the art will readily understand, each radio frame comprisesan E-UTRA radio frame comprising ten subframes 142, 144, a number ofwhich are reserved for Multi-Media Broadcast over a Single FrequencyNetwork (MBSFN). In FIG. 14, the subframes reserved for MBSFN arereferred to as MBSFN subframes 144.

To allow legacy mobile communication devices to communicate successfullyin the system 131, the non-MBSFN subframes 142 comprise legacy E-UTRAsubframes having a legacy PDCCH (e.g. as defined in the relevant 3GPPrelease 8, 9 or 10 standards). Thus, older (e.g. release 8, 9 and 10)mobile communication devices are advantageously able to monitor thelegacy PDDCH in the non-MBSFN subframes 142.

The MBSFN subframes 144 are configured with a BFed PDCCH with acorresponding new DMRS pattern, as described previously. Newer (e.g.release 11 and beyond) mobile communication devices 3, such as thoseshown in FIG. 13, are advantageously able to monitor both the legacyPDDCH in the non-MBSFN subframes 142 and the BFed PDCCH in the MBSFNsubframes 144.

Referring to FIG. 15, there are a number of different options (labelled(a) to (c) in FIG. 15) for MBSFN subframe configuration for the systemof FIG. 13. In the first option (a), the MBSFN subframes 144 of both themacro base station 5-1 and the pico base stations 5-2, 5-3 are providedwith the BFed PDCCH. This option has the advantage of simplicity and thefact that beamformed control channels 4-1, 4-2, 4-3, 4-5, 4-8 can beused in both the pico and macro cells 7, 9.

In the second option (b), the MBSFN subframes 144 of both the macro basestation 5-1 and the pico base stations 5-2, 5-3 are provided with apartitioned BFed PDCCH region and PDCCH-less region (similar to thatdescribed with reference to FIG. 10). The regions are generally equalsized and are partitioned such that the BFed PDCCH region for the macrocell 7 does not overlap with the BFed PDCCH region for the pico cell 8.This option reduces the risk of interference and allows beamformedcontrol channels 4-1, 4-2, 4-3, 4-5, 4-8 to be used in both the pico andmacro cells 7, 9.

In the third option (c), the MBSFN subframes 144 of the of the pico basestations 5-2, 5-3 are provided with a BFed PDCCH region, whilst theMBSFN subframes 144 of the macro base station 5-1 are not. This optionreduces the risk of interference and allows beamformed control channels4-3, 4-8 to be advantageously used in the pico cells 9 (for this option,the macro base station 5-1 does not use the beamformed control channelslabelled 4-1, 4-2, 4-5 shown in FIG. 13).

Application in a Distributed Antenna System

FIG. 16 schematically illustrates a mobile (cellular) telecommunicationsystem 161 in which a user of any of a plurality of mobile communicationdevices 3-1 to 3-7 can communicate with other users via a macro basestation and a local antenna 15-0 at the base station and a plurality ofgeographically distributed antennas 15-1, 15-2 and 15-3. Eachdistributed antenna 15-1 to 15-3 is connected to the base station (forexample by a fibre optic link) and the base station 5 controls receptionand transmission via the antenna 15. The base station 5 uses a commoncell identity for communications via each antenna 15 and hence a mobilecommunication device 3 being served by any one of the antenna 15 behavesas if it is operating in a single cell.

In FIG. 16, the base station effectively operates, on a first componentcarrier C1, a single ‘common’ primary cell (PCell) 7 that comprises aplurality of primary sub-cells 7-0 to 7-3 each provided using adifferent respective antenna 15-0 to 15-3. The base station operates, ona second component carrier C2, an effective secondary cell (SCell) 8that comprises a plurality of secondary sub-cells 8-0 to 8-3 eachprovided using a different respective antenna 15-0 to 15-3.

In the example shown, the ‘local’ or ‘master’ primary sub-cell 7-0operated via the local antenna 15-0 has a larger geographical coveragethan the ‘local’ or ‘master’ secondary sub-cell 8-0 operated via thelocal antenna 15-0. The geographical coverage of each of the‘distributed’ sub-cells 7-1 to 7-3 and 8-1 to 8-3 operated via thedistributed antennas 15-1 to 15-3 falls completely within thegeographical coverage of the local primary sub-cell 7-0 and overlapspartially with the geographical coverage of the local secondary sub-cell8-0. The power of the carriers C1, C2 used to provide the distributedsub-cells 7-1 to 7-3 and 8-1 to 8-3 is set such that the geographicalcoverage of the distributed primary sub-cells 7-1 to 7-3 (of thisexample) are substantially co-incident with the geographical coverage ofthe distributed secondary sub-cells 8-1 to 8-3. In the example shown thedistributed sub-cell 7-2, 8-2 provided using distributed antenna 15-2partially overlaps with the distributed sub-cells 7-1, 7-3, 8-1, 8-3respectively provided using the other distributed antennas 15-1, 15-3.It will be apparent, therefore, that there is a potential for relativelyhigh control channel to control channel interference between thesub-cells 7, 8 where they overlap with one another.

In this exemplary embodiment, PDCCH to PDCCH interference on the primarycomponent carrier C2 may be avoided by appropriate time domainseparation of the sub-frames used to communicate the PDCCH (e.g. withABS for the other sub-frames as described previously).

Referring to FIG. 17, in which the subframe configuration for thecomponent carriers for the distributed cells is illustrated, controlchannel to control channel interference on the secondary carrier C2 isavoided by providing a different control channel (DMRS based PDCCH),each having a different respective DMRS sequence, in the control regionsof respective subframes for overlapping distributed secondary subcells8-1 to 8-3. The DMRS sequence selected for the different DMRS basedPDCCHs is selected to be substantially orthogonal.

As shown in FIG. 17, a DMRS based PDCCH having a first DMRS sequence(DMRS based PDCCH 1) is provided in the control region of subframescommunicated in the non-overlapping secondary subcells 8-1 and 8-3provided via antennas 15-1 and 15-3. A DMRS based PDCCH having a secondDMRS sequence (DMRS based PDCCH 2) is provided in the control region ofsubframes communicated in the secondary subcell 8-2, provided viaantenna 15-2, that overlaps with the other secondary subcells 8-1 and8-2, thereby helping to avoid control channel to control channelinterference in the regions in which the secondary subcells 8 overlap.

The structure of each DMRS based PDCCH is, therefore, similar to that ofthe BFed PDCCH of earlier examples. However, in this embodiment, the newPDCCH is transmitted from a single antenna and is omnidirectional ratherthan beamformed. The structure of the DMRS based PDCCH is, thereforesimilar to the BFed PDCCH as transmitted from a single antenna port.

Other Modifications and Alternatives

Detailed embodiments have been described above. As those skilled in theart will appreciate, a number of modifications and alternatives can bemade to the above embodiments and variations whilst still benefitingfrom the inventions embodied therein.

It will be appreciated that although the macro and the pico basestations 5 have each been described with particular reference to adifferent set of modules (as shown in FIGS. 4 and 5) to highlight theparticularly relevant features of the different base stations 5, themacro and the pico base stations 5 are similar and may include any ofthe modules described for the other. For example, each pico base station5-2, 5-3 may include a measurement management module 445, a directiondetermination module 447 and/or a beamforming module 449 as describedwith reference to FIG. 4. Similarly, the macro base station 5-1 mayinclude a cell type identifier module 547 as described with reference toFIG. 5.

It will be appreciated that although the communication system 1 isdescribed in terms of base stations 5 operating as macro or pico basestations, the same principles may be applied to base stations operatingas femto base stations, relay nodes providing elements of base stationfunctionality, home base stations (HeNB), or other such communicationnodes.

In the above embodiments, the cell type identifier module has beendescribed as providing information for identifying the cells controlledby the base station 5-2, 5-3 as pico cells 9, 10 and that thisinformation is broadcast to mobile communication devices 3 that comewithin or close to the coverage area of the pico Pcell 9. It will beappreciated that the information for identifying the cells provided bythe base station 5-2, 5-3 may comprise any suitable information such asa specific cell type identifier information element, or a cell identity(Cell ID) from which cell type can be derived. For example, if a HeNB,rather than a pico base station, operates the low power cells 9, 10, thecell type can be identified from comparing the cell identity provided bythe HeNB to a range of Cell IDs known to be allocated to HeNBs.

Further, whilst in the above description it is the mobile communicationdevice that determines whether a particular cell is a pico cell forwhich control channel interference is a risk, the macro base stationcould also do this. For example, the macro base station may mandate anymobile communication device configured with a BFed PDCCH, to carry outRSRP measurements and to compare the results with predefined thresholdvalue (e.g. similar to the ‘trigger’ threshold as described). If theresults are found to be above that threshold value, the mobilecommunication device simply reports the measurement to the base stationwith cell identity information (e.g. the Cell ID) for the cell to whichthe measurements relate. On receipt of the report, the macro basestation (which has access to information identifying the cell IDs forthe pico cells in its coverage area) can avoid using a BFed PDCCH for amobile communication device that is close to a pico cell within itscoverage area. In the case of HeNBs, the macro base station is able toidentify them, based on their cell IDs, so that the macro base stationcan avoid using the BFed PDCCH for a mobile communication device that isclose to an identified HeNB cell.

Referring to the embodiment described with reference to FIG. 1, whilst aBFed PDCCH is not provided for the extension component carrier C1 of thepico SCells 10-2, 10-3, it will be appreciated that such a BFed PDCCHcould potentially be provided, albeit at the possible expense ofinterference between the PDCCH of the macro PCell 7 and the BFed PDCCHof the pico SCell 9. It will also be appreciated that whilst it has notbeen described in significant detail above, a BFed PDCCH of any of thecommunication systems could potentially be used for cross carrierscheduling for any component carrier of that system regardless ofwhether or not a control channel is provided for that component carrier.

Whilst a particular DMRS pattern has been described for the BFed PDCCHany suitable DMRS pattern may be used that is different to that used fora legacy PDCCH.

It will be appreciated that the predetermined trigger threshold may bereconfigurable. Further, the trigger threshold may be adaptive, forexample to allow it to change automatically, or semi-automatically,based on prevailing radio conditions. The threshold value, and timing ofthe trigger message, may vary in dependence on the implementation. Theoptimum threshold value for different situations may be arrived at basedon simulation.

Where a flow chart shows discrete sequential blocks, this is for thepurposes of clarity only and, it will be appreciated that many of thesteps may occur in any logical order, may be repeated, omitted, and/ormay occur in parallel with other steps. For example, referring to stepS4 of the flow chart of FIG. 7, the pico base stations may broadcastidentification periodically, in parallel with the other of the stepsshown. Similarly, steps S4 and S5 need not be repeated every iterationof loops L1 and L4. Further, the mobile communication device 3 maymonitor the RSRP of received reference signals continuously in parallelwith the other steps.

Although the provision a beamformed PDCCH has been described in detailit will be appreciated that other information, deliberately omitted fromtransmission on an extension carrier, may also be provided in abeamformed manner on extension carriers. For example a new beamformedPhysical Hybrid ARQ Indicator Channel (BFed PHICH) may also be providedon the extension carrier.

Although the terminology used refers to a beamformed PDCCH (BFed PDCCH),any similar terminology may be used appropriately to refer to a newbeamformed PDCCH and/or a PDCCH having a modified DMRS (for example‘Precoded PDCCH’, ‘DMRS-based PDCCH’, ‘Codebook based beamformingPDCCH’).

The beamforming may be codebook based in which a ‘precoding’ vector (forweighting the transmissions from respective antennas) is selected from aset of predefined precoding vectors (the ‘codebook’). In this case themobile communication device either knows, or is informed of, theprecoding vector used. The beamforming may be non-codebook based inwhich the network applies arbitrary beamforming at the transmitter andthe mobile communication device has no immediate means for determiningthe nature of the beamforming that has been applied. In this case amobile communication device specific reference signal to which the samebeamforming has been applied is transmitted to allow estimation of thechannel experienced by the beamformed transmission. The pico and macrobase stations may respectively use different beamforming techniques(e.g. the pico base station may use codebook based beamforming or andthe macro base station may use non-codebook based beamforming or viceversa).

In the example described with reference to FIG. 13, the BFed PDCCH wasdescribed as being provided in the MBSFN subframes of a radio framewhilst the legacy PDCCH was placed in other subframes. It will beappreciated that whilst using the MBSFN subframes is advantageous interms of simplicity of implementation, any appropriate predeterminedsubframes may be used (for example ABS subframes). In a particularlyadvantageous scenario for example, the subframes used for BFed PDCCHtransmission use MBSFN subframes that are also configured to be ABSsubframes. The benefits of this arise because MBSFN subframes arestandardised for 3GPP, Release 8 mobile communication devices, and ABSsubframes are standardised for 3GPP Release 10 mobile communicationdevices. Thus, for backward compatibility, Release 8 mobilecommunication devices are able to interpret MBSFN subframes, and Release10 mobile communication devices are able to interpret both MBSFN and ABSsubframes. Accordingly, having MBSFN subframes carrying the new BFedcontrol channel as a subset of subframes configured for Almost BlankSubframes (ABS) means that the legacy Release 10 mobile communicationdevices will be able to effectively ignore them as ABS subframescarrying no data, Release 8 mobile communication devices will be able totreat them as MBSFN subframes and newer mobile communication devices, asdescribed for the above embodiments, will be able to treat them as BFedPDCCH carrying sub-frames.

Furthermore, in the example described with reference to FIG. 13, byusing co-ordinated scheduling in which the macro base station 5-1 andpico base station 5-2, 5-3 exchange information on when the BFed PDCCHis to be scheduled, collision between the BFed PDCCHs transmitted bythose base stations 5 can be avoided.

In yet another advanced variation of the example described withreference to FIG. 13, the macro base station 5-1 and pico base station5-2, 5-3 can use the same resource for BFed PDCCHs where orthogonalcommunication streams are applied based on CSI information exchangedbetween the macro base station 5-1 and pico base station 5-2, 5-3.

In the exemplary embodiments described above, each new control channelhaving a new DMRS pattern has been described as being provided in acontrol region of a subframe. It will be appreciated that whilst this isparticularly beneficial, the control channel could be provided in a dataregion of a subframe or partially in a control region and partially in adata region whilst still benefiting from many of the advantages providedby the invention. Nevertheless, despite the fact that there may be areluctance to reuse a region normally reserved for the existing PDCCHbecause of the perceived technical difficulties in doing so, providingthe new control channel(s) having the new DMRS in the control region, asopposed to the data region does provide some notable advantages.Firstly, for example, decoding a control channel in the region of asubframe reserved as a control region is significantly quicker thandecoding a control channel in the region of a subframe reserved as adata region because mobile communication devices look at the controlregion before the data region. Secondly, for similar reasons, decoding acontrol channel in the region of a subframe reserved as a control regionuses less battery power than decoding a control channel in the region ofa subframe reserved as a data region. Further, when no data resourcesare allocated by the control channel, having the control channel in thecontrol region allows the mobile communication device to ignore the dataregion completely, with the power and speed advantages that follow fromsuch an arrangement.

In the above exemplary embodiments, a mobile telephone basedtelecommunications system was described. As those skilled in the artwill appreciate, the signalling techniques described in the presentapplication can be employed in other communications system. Othercommunications nodes or devices may include user devices such as, forexample, personal digital assistants, laptop computers, web browsers,etc. As those skilled in the art will appreciate, it is not essentialthat the above described relay system be used for mobile communicationsdevices. The system can be used to extend the coverage of base stationsin a network having one or more fixed computing devices as well as orinstead of the mobile communicating devices.

In the exemplary embodiments described above, the base stations 5 andmobile communication devices 3 each include transceiver circuitry.Typically, this circuitry will be formed by dedicated hardware circuits.However, in some exemplary embodiments, part of the transceivercircuitry may be implemented as software run by the correspondingcontroller.

In the above exemplary embodiments, a number of software modules weredescribed. As those skilled in the art will appreciate, the softwaremodules may be provided in compiled or un-compiled form and may besupplied to the base station or the relay station as a signal over acomputer network, or on a recording medium. Further, the functionalityperformed by part or all of this software may be performed using one ormore dedicated hardware circuits.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

1. A mobile communication device configured to communicate with a communication apparatus, the mobile communication device comprising: a controller and a transceiver, wherein the controller is configured to: control the transceiver to receive a first demodulation reference signal (DMRS) transmitted from the communication apparatus using at least one resource element on at least one of first two antenna ports of a plurality of antenna ports, wherein the first DMRS is associated with transmission of a first physical downlink control channel (PDCCH) transmitted using the at least one of the first two antenna ports of the plurality of antenna ports; control the transceiver to receive a second DMRS transmitted from the communication apparatus using at least one resource element on at least one of second two antenna ports of the plurality of antenna ports, wherein the second DMRS is associated with transmission of a second PDCCH transmitted using the at least one of the second two antenna ports of the plurality of antenna ports; in a case where the first PDCCH is transmitted using the at least one of the first two antenna ports, demodulate the first PDCCH based on the first DMRS; and in a case where the second PDCCH is transmitted using the at least one of the second two antenna ports, demodulate the second PDCCH based on the second DMRS.
 2. A communication apparatus configured to communicate with a mobile communication device, the communication apparatus comprising: a controller and a transceiver, wherein the controller is configured to: control the transceiver to transmit, to the mobile communication device, a first demodulation reference signal (DMRS) using at least one resource element on at least one of first two antenna ports of a plurality of antenna ports, wherein the first DMRS is associated with transmission of a first physical downlink control channel (PDCCH) transmitted using the at least one of the first two antenna ports of the plurality of antenna ports, control the transceiver to transmit, to the mobile communication device, a second DMRS using at least one resource element on at least one of second two antenna ports of the plurality of antenna ports, wherein the second DMRS is associated with transmission of a second PDCCH transmitted using the at least one of the second two antenna ports of the plurality of antenna ports; in a case where the first PDCCH is transmitted using the at least one of the first two antenna ports, modulate the first PDCCH based on the first DMRS; and in a case where the second PDCCH is transmitted using the at least one of the second two antenna ports, modulate the second PDCCH based on the second DMRS.
 3. A communication control method in a mobile communication device which communicates with a communication apparatus, the communication control method comprising: receiving a first demodulation reference signal (DMRS) transmitted from the communication apparatus using at least one resource element on at least one of first two antenna ports of a plurality of antenna ports, wherein the first DMRS is associated with transmission of a first physical downlink control channel (PDCCH) transmitted using the at least one of the first two antenna ports of the plurality of antenna ports; control the transceiver to receive a second DMRS transmitted from the communication apparatus using at least one resource element on at least one of second two antenna ports of the plurality of antenna ports, wherein the second DMRS is associated with transmission of a second PDCCH transmitted using the at least one of the second two antenna ports of the plurality of antenna ports; in a case where the first PDCCH is transmitted using the at least one of the first two antenna ports, demodulating the first PDCCH based on the first DMRS; and in a case where the second PDCCH is transmitted using the at least one of the second two antenna ports, demodulating the second PDCCH based on the second DMRS.
 4. A communication control method in a communication apparatus which communicates with a mobile communication device, the communication control method comprising: transmitting, to the mobile communication device, a first demodulation reference signal (DMRS) using at least one resource element on at least one of first two antenna ports of a plurality of antenna ports, wherein the first DMRS is associated with transmission of a first physical downlink control channel (PDCCH) transmitted using the at least one of the first two antenna ports of the plurality of antenna ports, transmitting, to the mobile communication device, a second DMRS using at least one resource element on at least one of second two antenna ports of the plurality of antenna ports, wherein the second DMRS is associated with transmission of a second PDCCH transmitted using the at least one of the second two antenna ports of the plurality of antenna ports; in a case where the first PDCCH is transmitted using the at least one of the first two antenna ports, modulating the first PDCCH based on the first DMRS; and in a case where the second PDCCH is transmitted using the at least one of the second two antenna ports, modulating the second PDCCH based on the second DMRS. 